1. Field of the Invention
The present invention relates to an image processing device and an image processing method which can be applied to image forming devices such as a digital copying machine, and a facsimile machine, and in which a conversion processing is performed on image signals.
2. Related Background Art
In general, in image forming devices such as a digital copying machine, and a facsimile device, first, light reflected by an original is received and converted to an electric signal by CCD, and the like, and a resulting analog luminance signal is converted to a digital luminance signal by A/D converter, and the like, so that a multivalued luminance signal of an original image is obtained.
Next, for example, by referring to a luminance/density conversion table prepared beforehand, the original image signal is converted to a multivalued image density signal based on luminance/density conversion information.
Moreover, it is assumed that a user desires to enlarge or reduce an image, and selects and sets an enlargement/reduction magnification by operating an external key or the like. In this case, after enlarging/reducing an image luminance signal, the signal is converted to a multivalued image density signal by referring to a luminance/density conversion table.
For example, an output density correction table is used to convert the resulting image density signal to the image density signal corresponding to a printer characteristic, and the converted image density signal is outputted via a printer. This is applied to the digital copying machine.
Moreover, the resulting image density signal is converted to the output density signal suitable for an image resolution, for example, using the output density correction table. Subsequently, the signal is converted to binary data, which is further subjected to a predetermined compression processing, and then transmitted to a reception device via a communication channel or the like. This is applied to the device on the facsimile transmission side.
Furthermore, depending on the type of the original image, the image density signal is set to have a higher density than the actual original density so that image quality is enhanced in some cases, and only a low density portion is set to have a dropped density as compared with the actual original density so that the image quality is enhanced in other cases.
For example, the former cases represent character originals, and the latter cases represent photograph originals. In this case, when the user sets the type of the original as a mode, the luminance/density conversion table, or the output density correction table is changed in accordance with the mode.
Moreover, based on the mode set by the user, a luminance/output density conversion table (a table to input luminance data and output density data) for the mode is first calculated from the luminance/density conversion table and the output density correction table to prepare LUT (lookup table). By referring to the data, data conversion is implemented for output or transmission. This is also known.
However, the above-described conventional examples have the following problems.
When the image is enlarged/outputted, by the enlarged image processing, the resolution of output image is apparently deteriorated as compared with the resolution of input image, so that the edge portion of the image signal is blurred.
This respect will be described with reference to FIGS. 14A to 14C. When the image of FIG. 14A is subjected to 200% enlargement (FIG. 14C), the image edge portion is also doubled, and the outputted image seems to be blurred.
Moreover, when the image is reduced/outputted, for intermediate-gradation density fine lines, and the like within the input image, the value of the output image signal is lowered by the reduced image processing in some cases.
These cases will also be described with reference to FIGS. 14A to 14C. When the image of FIG. 14A is subjected to 50% reduction (FIG. 14B), assuming that the output resolution is doubled as compared with the reading resolution, the image edge portion also becomes half, so that the intermediate gradation area in the outputted image is largely decreased.
In this case, if the reading resolution is substantially equal to the output resolution, the image is thinned out, so that the intermediate gradation is eliminated in some cases.